1. Field of the Invention
The present invention relates to adjusting a center frequency of a filter, and more particularly, to a method and an apparatus for adjusting a center frequency of a surface acoustic wave (SAW) filter used for extracting information carried via a television (TV) channel.
2. Description of the Prior Art
The Digital Video Broadcasting-terrestrial (DVB-T) standard has been adopted by many countries. However, the bandwidths of broadcasting signals among different regions in the world are different, and it is known that at least four bandwidths 5 MHz, 6 MHz, 7 MHz, and 8 MHz are adopted for video broadcasting at the present time. Therefore, if a product (i.e. a TV) designed for a single bandwidth is used in a region using a different bandwidth, this may result in reduced video quality or even an unwatchable video signal. There are two prior art methods for solving this problem; a first method is that a tuner uses several different SAW filters respectively having different bandwidths to receive video broadcasting signals with different bandwidths. As several SAW filters are used, however, and the SAW filter is expensive, employing several SAW filters in the tuner results in higher cost on production line management and materials. The second method is that a single SAW filter having a maximum bandwidth among signal bandwidths available for TV signal transmission is used in the tuner to guarantee that a required signal will not be filtered out. When the bandwidth of the video broadcasting signal is less than the bandwidth of this SAW filter, however, the SAW filter cannot filter out adjacent channel interference (ACI) and the video quality may be seriously influenced and degraded.